1. Field of the Invention
The present invention relates to a chain guide that guides a traveling chain.
The chain guide is provided in a chain drive system, and the chain drive system is, e.g., a timing chain drive system used in an engine of an automobile or the like.
2. Description of the Related Art
Conventionally, a chain guide having a shoe with which a traveling chain is in sliding contact and a base that supports the shoe is formed by assembling the shoe and the base together (e.g., see Japanese Patent Application Laid-open No. 2009-36275 (paragraphs 0023 to 0034, all drawings)).
In the chain guide in which the base and the shoe are assembled together, depending on an environment temperature at which the chain guide is used, the shoe expands or contracts in a longitudinal direction of the guide relative to the base due to a difference in thermal expansion/contraction amount in the longitudinal direction of the guide between the base and the shoe. In this case, for example, when the shoe contracts in the longitudinal direction of the guide with respect to the base, if the contraction of the shoe is restricted by the base, a load in the longitudinal direction of the guide (hereinafter referred to as a “restriction load”), e.g., a tensile load acts on the shoe. At this point, if the rigidity of the shoe is small, there are cases where the shoe is damaged by the tensile load when it is increased.
To cope with this, by providing a clearance for absorbing the expansion and contraction of the shoe between the base and the shoe in the longitudinal direction of the guide, the generation of the tensile load is prevented when the shoe expands or contracts within the range of the clearance and, even when the shoe expands or contracts beyond the range of the clearance, the magnitude of the tensile load acting on the shoe is small as compared with a case where the clearance is not provided, and hence it is possible to prevent the damage to the shoe by the tensile load.
However, in a case where the chain guide is unusually or temporarily used at an environment temperature lower or higher than a preset environment temperature due to its use environment, the increased restriction load acts on the shoe, and hence there has been a problem that the durability of the shoe is reduced.
In addition, a force resulting from friction with the chain (hereinafter referred to as a “chain external force”) acts on the shoe with which the chain is in sliding contact in a traveling direction, in a counter-traveling direction, or in a width direction of the guide in response to the traveling state of the chain. Further, a force based on the chain external force acts on the engagement portion of the shoe that holds the shoe to the base, and hence it is desirable to improve the capability of the engagement portion to hold the shoe to the base in order to stabilize the travel of the chain in the chain guide.
Further, in a case where a pair of guide side walls provided in the base are used in order to prevent a phenomenon in which the shoe is moved in the width direction of the guide by the chain external force (hereinafter referred to as a “lateral movement phenomenon”), the type of the base to which the shoe having the engagement portion for holding the shoe to the base is assembled is limited. Consequently, there has been a secondary problem that the type of the base to which the shoe can be assembled is limited such as a case where the shoe having the engagement portion cannot be used for the base without the guide side wall.